Scanning corner array antenna



Aug. 24, 1965 A. c. SCHELL 3,202,997

SCANNING CORNER ARRAY ANTENNA Filed Oct. 16. 1961 5 Sheets-Sheet 1INVENTOR. HAMA/Y l @6V/16,6

Aug. 24, 1965 A. c. SCHELL 3,202,997

SCANNING CORNER ARRAY ANTENNA Filed Oct. 16, 1961 5 Sheets-Sheet 2 Aug.24, 1965 A. c. scHELL SCANNING CORNER ARRAY ANTENNA 5 Sheets-Sheet 3Filed Oct. 16, 1961 INVENTOR. H664 C. 527145616 ULM da( uw l?. 711

A. C. SCHELL SCANNING CORNER ARRAY ANTENNA Aug. 24, 1965 5 Sheets-Sheet4 Filed Oct. 16, 1961 INVENTOR. /V 6. STA/l LUL@ Aug. 24, 1965 A. c.SCHELL 3,202,997

SCANNING CORNER ARRAY ANTENNA Filed OCT.. 16, 1961 5 Sheets-Sheet 5 UMDMMR. 711 m79 United States Patent O 3,?.ti27 SCANNING CORNER ARRAYANTENNA Allan C. Schell, Medford, Mass., assigner to the United Statesof America as represented by the Secretary of the Air Force Filed Giet.16, 1961, Ser. NdT-45,519 3 'Claims (Cl. 343-814) (Granted under Title35, US. Code (1952), sec. 266) The invention described herein may bemanufactured and used by or for the United States Government forgovernmental purposes without payment to me of any royalty thereon.

'i his invent-ion relates generally to apparatus for radiating andreceiving ultra high frequency electromagnetic waves, and moreparticularly to a directive, corner reliector antenna system wherebyscanning within the corner may be accomplished without physical movementof the reector structure.

The corner reector antenna has many characteristics which make it anattractive means for transmitting electromagnetic waves. Thesecharacteristics include high gain, low back radiation, good directivity,wide bandwidth, and constructional simplicity. The use of such anantenna, however, has been limited to applications where the dimensionsof the reflector aperture approximate one or two wavelengths, and thecorner angle is either sixty or ninety degrees. A further vexing, andheretofore unsolved problem, is the mechanical diiiiculty encountered4in scanning with this type of antenna. Due to the large size of thecorner antenna, especially at frequencies on the lower end of the radiospectrum, physical movement of the antenna structure is extremelydifficult.

Because of the limited utility of the conventional corner reflectorantenna, various alternate schemes are resorted to whenever moredirectivity and gain are desired, or whenever specifications call for aparticular beam conliguration. The most common of said alternate schemesare the horn antenna, the parabolic reector antenna, and the dipolearray antenna. All are more diicult to construct than the cornerreiiector antenna, and are consequently more expensive. The horn antennahas the additional disadvantages of being inliexible, and extremelylarge at low frequencies. The dipole array antenna is subject to highback radiation and is, therefore, unsatisfactory for most militaryapplications. The consequent increase in physical size of each of theseantennae with the reduction of frequency, as in the case of the cornerreflector antenna, accentuates the problem of moving the large structurefor scanning purposes.

In my co-pending patent application entitled Corner Array Antenna,Serial No. 24,184, now abandoned, l have disclosed a novel cornerreflector antenna in which there is placed a plurality of dipole feedelements disposed at discrete points along the bisector of the cornerangle. The design of a corner antennae of greatly enhanced utilityhaving any desired beam configuration is made possible by the principlestaught therein. The present invention is a further improvement on thecorner angle reflector antenna, whereby the problem of scanning withlarge cumbersome antenna structure is effectively resolved.

lt is accordingly the primary object of my invention to provide a cornerreiiector antenna capable of scanning within the area defined by thereflecting surfaces without physical movement of the antenna structure.

lt is another object of my invention to provide an ultra high frequencyantenna of simple construction having high gain, a high degree ofdirectivity, wide bandwidth, Aa steerable beam, and low back radiation,said antenna being adaptable to a wide range of applications.

lt is still another object of my invention to provide a novel cornerreector antenna having a wider range of application and greater utilitythan has heretofore been possible.

it is a still further object of my invention to provide a cornerreflector antenna having a high degree of directivity and gain.

lt is a still further object of my invention to provide a cornerrefiector antenna adapted to produce substantially any speciiied beamconfiguration in combination with means for sweeping said beam withinthe confines of said reflecting surfaces.

It is a still further object of my invention to provide an ultra highfrequency electromagnetic wave antenna cornprising a corner reiiectorstructure in combination with a multiple dipole feed.

it is a still further object of my invention to provide means forradiating a high frequency electromagnetic wave, said wave having anarrow beam width, low sidelobe pattern commensurate with the size ofthe antenna.

These and other objects and advantages of the present invention willbecome more apparent by reference to the following description taken inconjunction with the accompanying drawings in which:

FIG. l illustrates a 60 corner angle reilector antenna having aplurality of dipole feed elements disposed at discrete points along thebisector of said corner angle;

FlG. 2 illustrates the field pattern produced by said 60 corner anglereflector antenna;

FlG. 3 illustrates the vertical field pattern produced by said 60 cornerangle reiiector antenna;

FIG. 4 illustrates azimuthal field patterns produced by said 60 cornerangle reflector antenna taken at elevation angles Of p:l5, 115:30?,q5:45 and I60 FlG. 5 illustrates the components of an olf-axis beam in acorner angle reiiector antenna for the values Fw),

FlG, 6 illustrates a corner angle reliector antenna adapted to produce afield pattern having sine terms;

FIG. 7 illustrates a 60 corner angle reflector antenna adapted to steerthe beam produced thereby within said corner angle;

FlG. 8 illustrates the radiation pattern of said steerable `beam at beamposition -0, 0:5", =lG, 0:15", and 02200;

FiG. 9 illustrate apparatus for controlling the directivity of saidbeam; and

FIG. l() illustrates an isometric view of one embodiment of myinvention.

My aforementioned co-pending patent application presents the `analysisof the corner antenna field pattern as a consideration of thereiiections of a plane wave incident upon the corner. A means forobtaining narrow-beamwidth low-sidelobe patterns commensurate with thesize of the antenna, said means involving the use of a number lof feedelements located along the bisector of the corner angle, is disclosedtherein. These elements produce higher-order terms of angular variationof the radiation pattern, and allow the synthesis of desired symmetricfunctions.

My present invention discloses, as an improvement thereon a novel meansfor producing sine terms in the radiation pattern of a corner reectorantenna. l have discovered that, by the proper combination of sine andcosine terms, it is possible to produce a narrow beam at substantiallyany angle within the corner angle. The sidelobes can be kept low duringthe beam-steering. This technique affords a method of electronicsteering of a lowsidelobe narrow beam within the sector angle.

The equations and their solutions for the electromageos qw] cos90+.94J15(17.2 cos 4 eos 156) netic fields generated by the subjectcorner reflector antennae disclosed herein are expressions representingthe inter-relationship of beam configuration, reflector geometry, numberand position of feed elements, phase and magnitude of the current onfeed elements, and frequency. General and specific application of theseexpressions will be illustrated whereby the several objects of myinvention are accomplished.

In the following calculations of eld patterns, the reflecting surfacesof the corner are considered to be planar, perfectly conducting, andinnite in extent. rThe angle between the two planes comprising thecorner is chosen to be a submultiple of 180, or 1r/N radians. Thepolarization of the transmitted or received wave is such that theelectric eld vector is parallel to the line of intersection of the twoplanes, denoted by the z direction. Symbolically, the corner angleisn/N, the distance from the apex to the feed elements is r, theelevation angle is p, the azimuth angles is 0, k is Zw/A, and ]n(kr) isthe Nth order Bessel function.

Under these conditions, the far field produced by a single currentelement located at a point on the bisector of the corner angle is Theextent to which a particular current generates one of the terms of thisseries is determined by the value of the corresponding Bessel function,and this is related to the distance of the elements from the apex inwavelengths. v

By placing several radiators along the bisector of the corner angle, itis possible to produce a radiation pattern of the form Ez-ZAmIm cos(2m-l-1)N0 (2) in the range -1r/2N01r/2N. In this manner, radiationfunctions even in 9, such as a narrow beam pointed along the cornerangle bisector, can be synthesized. An estimate of the size of theconducting planes for a given beamwidth of a uniform illuminationpattern is wavelengths between the edges of the ground planes, and

11:0.73 amps, [2z- 1.17 amps, and 13:0.94 amps respectively. Saiddipoles are located on the bisector of said corner angle at thedistances from the intersection of said reflecting surfaces.

rl`hese elements produce a beam with ZO-db uniform sidelobes in the H orazimuthal (=0) plane. It is necessary, however, to examine the radiationpattern at various elevation angles in order to be sure that there z areno large high-angle lobes. The complete description of the eld is givenby the equation cos sin 6) cos qb Curve 22 of FIG. 3 presents a verticalcut through the radiation pattern of 6:0 t0 show the behavior of themain beam as a function of elevation angle.

This pattern illustrates the directivity obtained in the vertical planeas the result of adding elements for horizontal plane beamwidthreduction. The use of a number of elements along the bisector of thecorner angle benefits principally the azimuthal or 6 plane pattern, butit should be remembered that the element positions may be chosen suchthat a desirable elevation pattern is also obtained.

The corner array thus has directivity in both planes and should not beconsidered a two-dimensional device. If additional colinearelements areused to narrow the elevation beamwidth, use should be made of theinherent properties of the corner. A considerable reduction in thenumber of necessary elements may result.

Azimuthal cuts through the radiation pattern for various elevationangles give additional information. First, any large, high-angle lobescan be found. Second, the frequency dependence of the pattern is shown.Apart from the element pattern, the elevation angle behavior of thecorner array is contained in the Bessel function argument kr cos p.Thus, azimuthal plots for a range of values of rp with k held constantmay also represent plots at a particular qb for different values of k(or A). The azimuth patterns for =0, 15, 30, 45, and 60 with )\=)\0 mayalso be viewed as plots of the azimuthal pattern at =0 or \0, 1.04k0,1.160, 1.41% and 2k. The azimuthal patterns of the array in FIG. 1 areshown for elevation angles of =15, 30, 45, and 60 by curves 23, 24, 25,and 26, respectively of FIG. 4. The effect of the higher-order termsdecreases with elevation angle; the pattern at =45, while reduced inmagnitude, has broadened because of the phase reversal of the fieldcomponent produced by the second element. The element impedances are ofcourse also a function of frequency. Y

The radiation patterns described thus far contain only odd cosinefunctions of N 0, that is, they are of the form To produce sine terms inthe radiation pattern it is necessary to position elements off thecorner angle bisector.

The expression for the corner antenna field is valid only in the range-1r/ZNS0S1r/2N. The argument of the rstterm in the series, cos N0,varies between and +90". The restriction of zero field at the conductingsurfaces prohibits even cosine terms in N0 from appearing; such termswould not be zero at ir/ZN. Similarly, any sine terms that are producedmust have arguments that are even multiples of N0 because odd multipleswould not go to zero at the conducting planes. The terms of angularvariation of the radiation pattern are therefore odd cosines and evensines. These may be written as Ez(0)= Z Am cos mN-I-Z Bm sin mN0 Ingeneral, it is desirable to synthesize patterns that can be put in theform A n=o Harmonics other than those of N0 need not be considered,since the pattern exists only in the sector qr/N. If this function isreversed and displaced by ar/N, it may be written Taking the differenceF(0)=20n cos nNtH- EDD sin nN (S) odd even From this it is possible todevelop a workable beam synthesis. Given a complete Fourier seriesapproximation of a desired function, the pattern obtained from thecorner will be the difference between the complete series of argument 6and the same series with the argument reversed and shifted by w/N. Forexample, consider the beam represented by curve 27 of FIG. 5. It may berepresented by N 17(0):2 An cos nN(6-00) N N :E An cos nil/'00 cos MVM-;A, sin nN sin nNQ Forming the difference F(0)=%F(e)-F(1f/N-e N N :W24 Acos MVM-00) -ZAD cos nNr/Nl-O-w) n=l n=l ZA', cos nil/'90 cos nN-l- AEA,sin 71H0., sin nNH Odd even (1G) the feeding coefficients An are seen tobe altered by cos nNo or sin nNo for the odd and even cases. The twopatterns Fw) and -Frr/NMH) are represented by curves 255 and Siti,respectively and the result 1W( 0) is represented by curve of FIG. 5.This function is Zero atie/2N.

A narrow beam with low sidelohes at an angle 00 from the bisector of thecorner, satisfying the conditions irnposed by the reflecting surfaces ofthe corner, can in this manner be obtained. By proper adjustment of thecurrents that produce the various terms a beam can be steered within thecorner angle.

The current and radiation pattern relations having thus been determined,it is possible to position the various sine and cosine-generatingelements. The odd cosine terms may be produced as previously described,'that is, elements may be located along the bisector of the corner anglein such a manner as to produce the even part of the desired function.Elements placed along the bisector do not change the symmetry of thedevice and therefore generate no sine terms; however, if two elements ofopposite polarity are symmetrically disposed on each side of the cornerangle bisector, only sine terms will result. The production of sineterms within the corner is accomplished with element pairs and maytherefore be done without involving the cosine-generating gelements.rThe first sine term needed is sin Zit/'0, and this suggests a corner offr/ZN radians. 6 shows a method of producing the sin 2N0 term. Each ofthe two elements 33 and is located on the bisector of one of the anglesformed by reflector surfaces and 323, and the corner angle bisector. Theresultant pattern is the same as that of a corner angle of fr/ZN,oriented at an angle of M4N to the 0:0 axis. Since two elements areused, this pattern exists in the entire corner of vr/N. This may bewritten as The next term of the series that is excited by elements 33,394 is sin 6N9; another set of elements is therefore necessary toproduce a sin 4N@ term. This may be done by using four additionalelements located at :hw/8N, i31r/8N, with adjacent elements oppositelyphased.

ti Such a scheme has the distinct advantage that no other lower-orderterms are produced, that is, four elements properly located along an arcgenerate sin 4N6, sin 12h70, and the feeding coeflicients for theseelements need not involve other terms,

The foregoing theory and concepts may now be applied to the design of ascanning corner array antenna in accordance with the principles andobjects of my invention, a specific embodiment of which is illustratedin FlG. 7.

The antenna design is developed from a determination of the LFouriercomponents of the corner reflector fields. The corner angle specied is60, and five terms of the antenna pattern are to be generated. These arecos 30, sin 66, cos 95, sin 120, and cos 150. As the beam is steeredwithin the sector, the feed currents must be varied Iaccording t0 thebeam angle. The elements of the array as illustrated in FlG. 7 comprisereiiector surfaces 35 and 36, and dipole feed elements 37 through 45.The distance r from the apex is chosen for each dipole feed element sothat the Bessel function associated with the .particular field componentis near a maximum, yand the other terms are small. In the presentexample r1=.64 t, @21.20% r3=l.58 r4=2.23h and r5=2.79?\. The angularvariation of the field pattern associated with each element is such thatIl, i3 and I5 excite cos 39 cos 90, and cos l5@ tennis respectively, I2excites the sin 60 term, and I4 excites the sin f2.6 term. The elementsthat produce the sin 126 pattern are interconnected so that only onecable is used for the control of this component. The same is true of thesin 60 pair. The manner in which the feed currents are varied in orderto produce a beam oriented at dincerent angles is given in the followingfeed coeicient table. The radiation patterns corresponding to these beampositions are illustrated by curves 46 through Si) of FIG. 8.

Feed Coecent table Beam Position 0 Cos 3 Sin 60 Cos 90 Sin 120 Cos 156(C1) (Dz) (Cs) (D4) (C5) l. 000 0. 000 l. 000 0. 000 l. O00 .956 500.707 856 259 865 .865 0. U00 .866 866 707 l. 000 707 0. C00 707 500 .866-1. 000 866 .500

The scanning corner array antenna constructed in accordance with theforegoing design antenna is shown in conjunction with its associatedbeam steering means in FIG 9. The antenna is supplied with plane 73 forconvenience in mounting the feed elements. @f the total of nine feedelements used, dipoles 37, d@ and 39 generate the cosine terms anddipoles through i5 generate the sine terms. The sine-generating elementsare connected by cables 5:3', 55, 57 and SS of one half wavelength sothat alternate elements are l out of phase. Power dividers 67 through70, attenuators E@ through 6?., and trombone phase Shifters d3 through@d are used to provide control over the iive inputs. Each element or setof elements used to produce a particular term in the radiation patternis preset by comparing its amplitude and phase with that of the cos 30element. The signal at each set of terminals is set at the Value shownin the accompanying table for the prescribed angle, and patterns aretaken without adiusting parameters for minimum beamwidth or lowsidelobes.

A perspective veiw of this particular embodiment of my invention isillustrated by Flr?. l0 wherein reflecting surfaces 35 and 36 are shownmounted at a 60 angle on mounting structure 75. There is also showndipole feed elements ffl-l5 and cables It is to be noted that theassociated beam steering means of FIG. 9 is not included with FlG. l0 asonly the perspective structure or" the corner antenna array is beingillustrated.

There has thus been disclosed a practical scanning corner reflectorantenna having high gain and a high degree of directivity wherein theseveral objects of my invention are accomplished. Although theparticular embodiment disclosed illustrates a sixty degree, nine feedelement device, it is not intended that the principles of my inventionas taught herein be restricted thereto. It will be apparent to thosehaving ordinary skill in the art that application of the principles ofmy invention will provide, within practical limits, scanning cornerreflector antennae having any degree of gain feed elements, or any sizecorner angle.

surfaces being positioned on mounting means located at the vertex of theangle formed thereby, a plurality of feed elements disposed inparallelism with said vertex, and with each other, in a series of planesdiverging from and including said vertex as a common access ofintersection of all said planes, all of said parallel feed elementsbeing located at discrete points along said several diverging planes andmeans for varying the currents applied to each of said feed elements. i2. A corner reflector antenna in combination with a plurality of dipolefeed elements, said dipole feed elements being disposed within saidcorner in parallelism along a series of planes having a common access ofintersection at said comer, and being adapted to divert the beamproduced thereby in response to the several currents applied to each ofSaid feed elements.

3. An electromagnetic Wave radiating device comprising a corner anglereflector, a rst series of feed elements disposed on the bisector ofsaid corner angle, a second series of feed elements disposed on thesub-bisectors of said corner angle all of said sub-bisectors having acom- .mon access of intersection at the vertex of said corner angle, andmeans for varying the phase and magnitude of the currents applied to theseveral elements of said first and second series of feed elements.

`4. An electromagnetic Wave radiating device in accordance with claim 3wherein said corner angle reector comprises two vertical intersectingplane surfaces of highly conductive material, and reflector mountingmeans.

5. An electromagnetic wave radiating device in accordance with claim 3wherein the individual elements of said first and said second series offeed elements are disposed n acaso? i at discrete distances from theapex of said corner angle such that the Bessel function associated withthe held `components produced thereby is substantially a maximum.

6. An electromagnetic wave radiating device in accordance with claim 3wherein said means for varying the phase and magnitude of the currentsapplied to said feed elements comprises a plurality of power dividers,said power dividers being adapted to provide a separate input currentfor each of the several feed elements, a plurality of phase shiftingdevices, means for controlling said phase shifting devices in accordancewith the desired radiation pattern and a plurality of attenuatingelements, said attenuating elements being adapted to control themagnitude of the current applied to each of said feed elements.

'7. An ultra high frequency antenna comprising a corner angle reflector,said corner angle reflector consisting of two vertically intersectingplane surfaces of highly conductive material, a first series of feedelements, said first series of feed elements bein" adapted to providecosine components of the eld pattern radiated thereby, a second seriesof feed elements, said second series of feed elements being adapted toprovide sine components of the field pattern radiated thereby, all ofsaid feed elements being located in planes having a common access ofintersection at the vertex of said corner angle, and means forcontrolling the phase and magnitude of the several currents applied tosaid first and said second series of feed elements.

S. A corner angle reflector antenna comprising two intersecting planesurfaces of highly conductive material, a plurality of cosine producingfeed elements, said cosine producing feed elements being disposed atdiscrete points on the bisector of the angle formed by the intersectionof said plane surfaces, a plurality of oppositely phased pairs of sineproducing feed elements,` the individual ele- Aments of each of saidpairs being disposed at discrete points on the sub-bisectors of saidangle formed by the intersection of said plane surfaces one on eitherside of said bisector, the intersection of said plane surfaces beingcoincident with the vertex of said corner angle, and means for varyingthe individual currents applied to said sine and said cosine producingfeed elements.

References Cited by the Examiner UNlTED STATES PATEIJTS 2,523,895 9/50Bailey 343-815 2,897,459 7/59 Stark 343-854 X 2,969,542 l/6l Coleman etal. 343-895 FOREIGN PATENTS 1,021,643 12/52 France.

HERMAN KARL SAALBACH, Primary Examiner.

1. A SCANNING ANTENNA COMPRISING TWO INTERSECTING PLANE SURFACES OFHIGHLY CONDUCTIVE MATERIAL, SAID PLANE SURFACES BEING POSITIONED ONMOUNTING MEANS LOCATED AT THE VERTEX OF THE ANGLE FORMED THEREBY, APLURALITY OF FEED ELEMENTS DISPOSED IN PARALLELISM WITH SAID VERTEX, ANDWITH EACH OTHER, IN A SERIES OF PLANES DIVERGING FROM AND INCLUDING SAIDVERTEX AS A COMMON ACCESS OF INTERSECTION OF ALL SAID PLANES, ALL OFSAID PARALLEL FEED ELEMENTS BEING LOCATED AT DISCRETE POINTS ALONG SAIDSEVERAL DIVERGING PLANES AND MEANS FOR VARYING THE CURRENTS APPLIED TOEACH OF SAID FEED ELEMENTS.